1. Field of the Invention
The present invention relates to an active matrix-type display panel driving device and a driving method for same.
2. Description of the Related Art
In recent years, electroluminiscent display devices (henceforth referred to as EL display devices) incorporating a display panel using organic electroluminiscent elements (henceforth referred to as EL elements) as light-emission elements carrying pixels have drawn considerable attention. Driving methods for panel displays using those EL display devices known in the prior art include simple matrix drives and active matrix drives. EL display devices with active matrix drives are advantageous in that they consume less power than simple matrix types, and have a smaller cross-talk between pixels, being especially appropriate for large-screen or high resolution displays.
FIG. 1 is a diagram showing the basic structure of an active matrix drive type EL display device.
As shown in FIG. 1, the EL display device comprises a display panel 10, and a driving device 100 to drive this display panel 10 according to an image signal.
The display panel 10 is constituted by an anode power line 16, a cathode power line 17, scanning lines A1 to An (scanning electrodes) constituting n horizontal scanning lines on one screen, and m data lines (data electrodes) B1 to Bm arranged in such a manner that they intersect each of the scanning lines A1 to An. Also, a drive voltage Vc is applied to the anode power line 16 and a ground potential GND is applied to the cathode power line 17. Furthermore, EL units E1, 1 to En,m bearing pixels are formed at each of the points of intersection of the scanning lines A1 to An and the data lines B1 to Bm in the above display panel 10.
FIG. 2 is a diagram showing the internal structure of an embodiment of an EL unit E formed at the intersection of one scanning line A and one data line B.
In FIG. 2, the gate G of a selective FET (Field Effect Transistor) 11 is connected to scanning line A and its drain D is connected to data line B. The gate G of a FET 12, the transistor for the light-emission drive, is connected to the source S of the FET 11. A drive voltage Vc is applied to the FET 12 through the anode power line 16, and a capacitor 13 is connected between the gate G and the source S. Further, the anode terminal of an EL element 15 is connected to the drain D of the FET 12. A ground potential GND is applied to the cathode end of the EL element 15 through the cathode power line 17.
The driving device 100, selectively applies scanning pulses in sequence to each scanning line A1 to An of the display panel 10. Also, the driving device 100 generates pixels data pulses DP1 to DPm according to the input image signal corresponding to each horizontal scanning line, with a timing synchronised with the application of the above scanning pulses, and applies them to the data lines B1 to Bm respectively. Each pixel data pulse DP has a pulse voltage according to the luminance level indicated by the input image signal. Now each EL unit connected to scanning line A to which a scanning pulse has been applied becomes the target for the writing of the pixel data. The FET 11 inside the EL unit E, which has now become the target for the writing of the pixel data, is placed in an on-state in response to the above scanning pulse and applies the above pixel data pulse DP, supplied through the data line B, to the gate G of the FET 12 and the capacitor 13, respectively. The FET 12 generates a light-emission drive current according to the pulse voltage of the pixel data pulse DP, and supplies it to the EL element 15. The EL element 15 emits then light according to this light-emission drive current with a luminance determined by the pulse voltage of the above pixel data pulse DP. Meanwhile, capacitor 13 charges according to the pulse voltage of the above pixel data pulse DP. By means of this charging action, the pulse voltage according to the luminance level indicated by the input image signal is held thus achieving the so-called pixel data writing. When released by the target for the writing of the pixel data, the FET 11 is placed in an off-state, and the supply of the pixel data pulse DP to the gate G of the FET 12 stops. In the meantime however, since the voltage held by capacitor 13 as described above continues to be applied to the gate G of the FET 12, the FET 12 keeps on sending continuously the above light-emission drive current to the EL element 15.
One of the features of the EL element 15 is that the resistance value of the element itself increases gradually after prolonged light-emission times. Since the frequency of light-emission is different in response to the input image signal for each EL element 15 in the EL units E1,1 to En,m supported by the display panel 10, differences in the accumulated light-emission time occur. Therefore, when the display panel 10 is driven for a prolonged time, the resistance value of the EL elements becomes non-uniform, causing a variance in light-emission luminance which results in problems such as an irregular luminance across the screen and screen burning.
An object of the present invention is to solve the above problems, by providing a display panel driving device and a drive method for same that can be used for a prolonged time and allows the display of high quality images without irregularity.
Also, since the light-emission frequencies as per the input image signal are different for each of the EL elements 15 within the above EL units E1,1 to En,m, differences in the accumulated light-emission time occur. Therefore, when the display panel 10 is driven for a prolonged time, the resistance value of the EL elements becomes non-uniform, causing a variance in light-emission luminance which results in problems such as an irregular luminance across the screen and screen burning.
The present invention further solves the above problems by providing a display panel driving device and a drive method for same which can permanently keep the luminance level within a given range across the screen, thus preventing the occurrence of luminance irregularity within the screen.
The display panel driving device according to a first aspect of the present invention is a display panel driving device for driving a display panel formed by a matrix-type arrangement of a plurality of emitting elements supporting pixels, the above display panel driving device comprising:
a drive voltage generator circuit which supplies a drive voltage through a power line to each of a plurality of emitting elements;
a current mesuring part for obtaining the current value corresponding to each pixel by fetching the value of current flowing in the above power line while causing each emitting element to independently emit light in succession, with the timing of the light-emission time of each emitting element, and to store it in a memory as the measured current value assigned to each pixel;
a luminance correction part for obtaining luminance-corrected pixel data by correcting the luminance level indicated by the pixel data of each pixel-corresponding to an input image signal, based on the above measured current value stored in the memory for the one pixel according to the pixel data; and
light-emission drive part for causing the above light-emission elements to emit light only for the period corresponding to the luminance-corrected pixel data during the image display light-emission periods in each frame period of the above input image signal.
Also, the display panel driving method according to the first aspect of the present invention is a display panel driving method for driving a display panel formed by a matrix-type arrangement of a plurality of emitting elements supporting pixels, the display panel driving method comprising the steps of:
a current measuring step for obtaining the current value corresponding to each pixel by fetching the value of current flowing in the above power line while causing each emitting element to independently emit light in succession, with the timing of the light-emission time of each emitting element;
a luminance correction step for obtaining luminance-corrected pixel data by correcting the luminance level indicated by the pixel data of each pixel corresponding to the input image signal, by means of the above measured current value stored in the above memory for the above one pixel according to the above pixel data; and
a light-emission drive step for causing the above light-emission elements to emit light only for the period corresponding to the above luminance-corrected pixel data in the image display light-emission periods within each frame period in the above input image signal.
The display panel driving device according to a second aspect of the present invention is a display panel driving device for driving, based on an input image signal, a display panel formed by a matrix-type arrangement of a plurality of emitting elements supporting pixels, the above display panel driving device comprising:
a drive voltage generator circuit which supplies a drive voltage through a power line to each of a plurality of emitting elements;
a current mesuring part for obtaining the current value corresponding to each pixel by fetching the value of current flowing in the above power line while causing each emitting element to independently emit light in succession, with the timing of the light-emission time of each emitting element, and to store it in a memory as the measured current value assigned to each pixel; and
drive voltage adjustment part for adjusting the voltage value of the above drive voltage
in such a manner that one value among each measured light-emission drive current value becomes equal to a predetermined reference current value.
The display panel driving device according to a third aspect of the present invention is a display panel driving device for driving, based on an input image signal, a display panel formed by a matrix-type arrangement of a plurality of emitting elements supporting pixels, the above display panel driving device comprising:
a drive voltage generator circuit which supplies a drive voltage through a power line to each of a plurality of emitting elements;
a current mesuring part for obtaining the current value corresponding to each pixel by fetching the value of current flowing in the above power line while causing each emitting element to independently emit light in succession, with the timing of the light-emission time of each emitting element, and to store it in a memory as the measured current value assigned to each pixel;
drive voltage adjustment part for adjusting the voltage value of the above drive voltage
in such a manner that one value among each measured light-emission drive current value becomes equal to a predetermined reference current value.
a luminance correction part for obtaining luminance-corrected pixel data by correcting the luminance level indicated by the pixel data of each pixel corresponding to the above input image signal, by means of the above measured current value stored in the above memory for the above one pixel according to the above pixel data; and
light-emission drive part for causing the above light-emission elements to emit light only for the period corresponding to the above luminance-corrected pixel data during the image display light-emission periods in each frame period of the above input image signal.
Also, the display panel driving method according to the second aspect of the present invention is a display panel driving method for driving, based on an input image signal, a display panel formed by a matrix-type arrangement of a plurality of emitting elements supporting pixels, the above display panel driving method comprising the steps of:
a current measuring step for obtaining the current value corresponding to each pixel by fetching the value of current flowing in the above power line while causing each emitting element to independently emit light in succession, with the timing of the light-emission time of each emitting element; and
a drive voltage adjustment step for adjusting the voltage value of the above drive voltage in such a manner that one value among each measured light-emission drive current value becomes equal to a predetermined reference current value.
Also, the display panel driving method according to the third aspect of the present invention is a display panel driving method for driving, based on an input image signal, a display panel formed by a matrix-type arrangement of a plurality of emitting elements supporting pixels, the above display panel driving method comprising the steps of:
obtaining the current value corresponding to each pixel by fetching the value of current flowing in the above power line while causing each emitting element to independently emit light in succession, with the timing of the light-emission time of each emitting element;
obtaining luminance-corrected pixel data by correcting the luminance level indicated by the pixel data of each pixel corresponding to the input image signal, by means of the above measured current value stored in the above memory for the above one pixel according to the above pixel data; and
causing the above light-emission elements to emit light only for the period corresponding to the above luminance-corrected pixel data during the image display light-emission periods in each frame period of the above input image signal.
A driving apparatus of a display panel according to the fourth aspect of the present invention is a driving apparatus of a display panel having a plurality of pixel portions arranged therein and each comprising a series circuit of a light light-emission element and a switch element, for driving the display panel in response to an input image signal, comprising: a drive voltage generator for applying a drive voltage to the series circuit of each of said plurality of pixel portions; a current measuring part for measuring a value of a current supplied from said drive voltage generator to the series circuit of each of said plurality of pixel portions; a current supplying part for adding to said current supplied from said drive voltage generator an off-set current component corresponding to a leak current of said display panel, and supplying a resultant current to the series circuit of each of said plurality of pixel portions; a memory control part for storing in memory a measured current value by said current measuring part at a light-emission timing correspondingly to each of said plurality of pixel portions while sequentially causing said light-emission element to singularly emit light for each of said plurality of pixel portions, by respectively turning on said switch element of each of said plurality of pixel portions; and a luminance corrector for correcting the light-emission luminance output of the light emitting device of each of said plurality of pixel portions based on a corresponding one of measured current values stored in said memory.
A driving method of according to the fourth aspect of the present invention is a display panel driving method for a display panel having a plurality of pixel portions arranged in a matrix form and each comprising a series circuit of a light-emission element and a switch element, for driving the display panel in accordance with an input image signal, comprising: applying an output drive voltage of a drive voltage generator to the series circuit of each of said plurality of pixel portions; supplying an addition value obtained by adding an off-set current component corresponding to a leak current of said display panel to said current supplied from said drive voltage generator, to the series circuit of each of said plurality of pixel portions; measuring a value of a current supplied from said drive voltage generator to the series circuit of each of said plurality of pixel portions; storing in memory a measured current value by measuring an output current value from said driving voltage generator at a light-emission timing correspondingly to each of said plurality of pixel portions while sequentially causing said light-emission element to singularly emit light for each of said plurality of pixel portions, by respectively turning on said switch element of each of said plurality of pixel portions; and correcting the light-emission luminance output of the light emitting device of each of said plurality of pixel portions based on a corresponding one of measured current values stored in said memory.